The present invention relates generally to frequency tunable semiconductor radiation-generating devices, such as lasers (e.g., tunable wire lasers), as well as methods for tuning frequency of such devices.
Frequency tunable lasers are employed in a variety of applications, such as spectroscopy, imaging (e.g., coherent optical tomography (OCT)), and sensing applications among others. Conventional techniques for tuning the frequency of a semiconductor laser can include, e.g., changing the refractive index of the lasing medium (e.g., via a change in its temperature) and/or changing the longitudinal mode profile of the laser radiation (e.g., via a change in the cavity length in external-cavity lasers).
The conventional laser frequency tuning techniques, however, suffer from a number of shortcomings. For example, the conventional frequency tuning methods are difficult to implement in lasers in which the wavelength of the laser radiation in the active medium is much larger than a cross-sectional dimension of the active medium. For example, the radiation wavelength of a laser operating in the terahertz region of the electromagnetic spectrum (e.g., a radiation wavelength in a range of about 30 microns to about 300 microns) can be significantly larger than a cross-sectional dimension of the active medium. The difficulties in tuning the frequency of terahertz lasers are evident in that continuous frequency tuning over a broad frequency range (e.g., greater than 100 GHz) using an external-cavity grating has yet to be achieved, and electrical tuning, e.g., by changing the refractive index due to temperature or due to a cavity-pulling effect, produces a relatively small fractional tuning (<1%).
Hence, there is a need for enhanced methods for tuning the frequency of semiconductor radiation-generating devices (e.g., terahertz lasers). There is also a need for enhanced semiconductor frequency tunable radiation-generating devices operating at wavelengths that are significantly greater than the cross-sectional dimension(s) of their active medium.